Bhagavad Gita · 17.17

श्रद्धया परया तप्तं तपस्तत्त्रिविधं नरैः।अफलाकाङ्क्षिभिर्युक्तैः सात्त्विकं परिचक्षते॥

śhraddhayā parayā taptaṁ tapas tat trividhaṁ naraiḥ aphalākāṅkṣhibhir yuktaiḥ sāttvikaṁ parichakṣhate

This threefold austerity — of body, speech, and mind — practiced with supreme faith by steadfast people who desire no reward, is said to be in the mode of goodness.

— Bhagavad Gita 17.17

Source: Sacred-Texts.com (Sanskrit) + Bhagavad-Gita.io (translations)